Conventional skateboard decks are manufactured out of plywood laminates using woods such as Canadian maple. Trucks are mounted on the front and rear ends of the bottom surface of the deck. Each truck includes a baseplate that is bolted directly to the deck, and an axle housing attached to the baseplate by a kingpin. The kingpin holds together the baseplate and axle housing. Wheels are attached to the respective ends of the axle housing. Decks are typically solid throughout, except for the truck mounting chambers. Rubber grommets are provided between the axle housing and baseplate, as well as below the axle housing, for shock absorption.
This conventional construction presents several problems. As discussed in U.S. Pat. No. 7,581,739, which is incorporated herein by reference, the rubber grommets of conventional trucks steadily deteriorate with use such that the shock absorption and performance of the trucks degrades quickly and is inconsistent over time. FIG. 5 illustrates a conventional rubber grommet truck suspension system 50 including rubber grommets 53 and 54 that dampen shocks and vibrations. Metal sleeves 55 and 56 cover respective grommets 53 and 54. Rubber grommet (bushing) 53 is provided between axle housing 51 and baseplate 52, and rubber grommet (cone bushing) 54 is provided between axle housing 51 and nut 57 of kingpin 58. Conventional kingpins are merely single piece bolts having a nut on one or both ends for adjusting tension. The kingpin is fixed in position. Rubber grommets act only to dampen shocks and minimize feedback into the skateboard deck. Conventional grommets act as dampers to dissipate shocks and vibrations from a user. The energy used to compress a grommet is largely dissipated. The grommets can also be worn down by friction and pressure, and thus may have difficulty in providing a durable and consistent user experience. The mechanical strain properties of rubber presents numerous deficiencies in skateboard performance. The response of rubber grommets differs between low and high strain rates (slow and fast forces). For example, in a low strain rate application where a user leans to one side on a skateboard, a gradual and steady force is applied to turn the trucks. In this case, the rubber gives and provides a smooth response, even if the rubber itself steadily deteriorates over time. However, in a high strain rate situation, where the truck goes airborne and the trucks impact the ground with high force, the fast response of rubber is to provide a hard impact that does not dissipate the force smoothly or gradually at all. In other words, rubber shows little elasticity with quick and forceful impacts. Therefore, the response, or mechanical strain, of rubber will vary depending on the speed and strength of the force. Also, a user may tend to favor one side of the board over the other, thereby creating uneven wear on the grommets, leading to inconsistent performance over time. Metal spring coils do not suffer from this difference in performance between low and high strain forces. In low and high strain rates, spring coils provide elasticity in absorbing and re-directing force in a consistent and smooth manner.
Another drawback of conventional designs is that in order to adjust nut 57 of kingpin 58, a user must hold the bolt head at one end and screw nut 57 at the other end. Therefore, adjusting truck 50 is a tedious process that is difficult to do in the field. When nut 57 is tightened at axle 51, kingpin 58 protrudes outward from axle 51, interferes with grinding and increases the overall height of the truck. The projection of kingpin 58 and nut 57 from axle housing 51 increases the overall height of the truck assembly.
U.S. Pat. No. 6,547,262 improves turn performance by shaping upper grommet 20 into a pulley-shape, but utilizes traditional urethane grommets and single-piece kingpins. Over time, one in the art would expect upper grommet 20 to wear unevenly and reduce pivoting performance. U.S. Pat. No. 7,104,558 is directed to a skateboard truck having a single-piece steel kingpin 40 rigidly fixed to a base 50, and including a head 41, shaft 45 with shoulder 42 and a threaded portion 44, as is typical.
In some conventional trucks, springs are incorporated as resistance members to control the wheel tilt and turning radius of the skateboard. The springs are mounted at a slight angle from the plane of the deck in order to control the degree of turning relative to a lateral force applied to the deck. For example, when a user's weight is shifted to the right or left side of the deck, the wheel axle of the truck will tilt relative to the deck, thereby changing the rolling direction of the wheels. Separate springs are typically provided on each side of the wheel axle. Different spring tensions will alter the turning radius of the skateboard by resisting lateral force. However, the use of springs in this manner increases the weight, cost and size of the trucks.